1. Field of the Invention
The present invention relates to a method for increasing the chemical and biological reactivity of cellulose. More particularly the invention relates to a method for increasing the digestibility of cellulose-containing feedstuffs, such as alfalfa, hay, wheat straw, wood fibers, corn stover, and the like, by ruminant animals.
In addition, the invention relates to a method for increasing the extraction of components such as protein from plant materials.
2. Description of the Prior Art
Many techniques have been used to increase the chemical and biochemical reactivity of cellulose. A number of factors influence cellulose reactivity, including particle size and fiber surface area, lignin content, cellulose crystallinity, etc. The techniques referred to can be characterized as either physical or chemical in nature. The physical treatments include ball-milling to very small mesh sizes, two-roll milling and attrition milling. These physical treatments are effective in producing a highly reactive and accessible cellulose. However, the power requirements for size reduction are so large as to make such treatments very costly. Chemical treatments include strong bases such as sodium hydroxide, strong acids, and various other cellulose swelling and dissolving agents such as the transition metal complex cellulose solvents. These chemical methods are also effective in producing highly reactive, accessible cellulose materials. These chemical agents have the disadvantage that they are expensive and must be recovered for reuse. Furthermore, many of these chemicals are toxic or inhibiting to biological systems such as are found in an alcohol fermentation facility or in the digestive tract of ruminant animals such as cattle, sheep, etc. Therefore, the removal of the chemical agents from the treated cellulose-containing material must be very complete. This further increases the expense of such chemical treatments. Furthermore, most such chemical agents are removed by washing with water. This has two major disadvantages: First, the water dilutes the cellulose-swelling or dissolving agent so that this chemical agent no longer effectively swells cellulose. Such chemical agents must be concentrated for reuse; this generally involves considerable capital equipment and operating expense. Second, water is known to promote the recrystallization of decrystallized cellulose. As cellulose recrystallizes, it becomes less and less reactive. Therefore, it is likely that the full effect of the decrystallizing or swelling agent is not obtained due to recrystallization caused by water. See Millet et al., "Pretreatments to Enhance Chemical, Enzymatic, and Microbiological Attack of Cellulosic Materials," Biotechnol. & Bioeng. Symp. No. 5, 193-219, (1975); and Millet et al. "Physical and Chemical Pretreatment for Enhancing Cellulose Saccharification," Biotechnol. & Bioeng. Symp. No. 6, 125-153 (1976). Millet et al. discuss various pretreatments of cellulosic materials, particularly woods and straw, to upgrade their digestibility, including swelling with alkaline agents such as sodium hydroxide, primary amines, aqueous or gaseous ammonia and anhydrous ammonia in both liquid and gaseous forms. They also discuss delignification, steaming of wood or straw to upgrade digestibility, as well as various physical treatments such as grinding, milling, irradiation, heating or compression.
Another treatment which involves both chemical and physical aspects is the so-called Masonite process wherein wood chips are saturated with water under pressure at about 300.degree.-500.degree. F. When the pressure is released, the water evaporates rapidly and the wood fibers tend to separate. This is similar to what occurs when the moisture inside a popcorn kernel evaporates violently and the kernel expands greatly. This process requires considerable expensive thermal energy in the form of steam. It has the additional disadvantage that some plant material is inevitably degraded and made less useful by the high temperatures required. Finally, the moisture content of the product is quite high, about 50%. See U.S. Pat. No. 3,707,436, issued Dec. 26, 1972, to J. J. O'Connor for "Exploding of Ammonia Impregnated Wood Chips;" U.S. Pat. No. 4,235,707, issued Nov. 25, 1980, to J. A. Burke, for Method and Apparatus for Treating Solid Municipal Refuse and Other Cellulose Containing Material; and U.S. Pat. No. 4,136,207, issued Jan. 23, 1979 to R. Bender, for "Method of Treating Lignocellulose Materials to Produce Ruminant Feed."